Liquid crystal display devices are increasingly used in watches, calculators, various measurement instruments, automobile panels, word processors, electronic organizers, printers, computers, televisions, clocks, advertising boards, etc. Representative examples of the liquid crystal display mode include twisted nematic (TN) mode, super twisted nematic (STN) mode, VA mode that is characterized by vertical alignment and use of thin film transistors (TFTs), and in-plane-switching (IPS)/FFS mode characterized by horizontal alignment. Liquid crystal compositions used in these liquid crystal display devices are required to be stable against external factors such as moisture, air, heat, and light, exhibit a liquid crystal phase in a temperature range as wide as possible with room temperature at the center, have low viscosity, and operate at low drive voltage. A liquid crystal composition is composed of several to dozens of compounds in order to optimize dielectric anisotropy (Δ∈) and/or refractive index anisotropy (Δn) and the like for each individual display device.
A vertical alignment display uses a liquid crystal composition with a negative Δ∈ and a horizontal alignment display such as a TN, STN, or IPS display uses a liquid crystal composition having a positive Δ∈. Recently, there has been a report of a drive mode with which a liquid crystal composition having a positive Δ∈ is aligned vertically in the absence of the applied voltage and a horizontal electric field is applied as in the IPS/FFS mode devices. There is now increasing need for liquid crystal compositions with positive Δ∈. Meanwhile, pursuit for lower voltage drive, high speed response, and wide operation temperature range is common for all driving modes. In other words, a positive Δ∈ with a large absolute value, low viscosity (η), and a high nematic phase-isotropic liquid phase transition temperature (Tni) are being required. Due to the setting of the product of Δn and the cell gap (d), i.e., Δn×d, the Δn of the liquid crystal composition must be adjusted to be in an appropriate range for the cell gap. Moreover, when the liquid crystal display device is to be adopted to televisions etc., high response speed is important and thus a liquid crystal composition with small γ1 is required.
Liquid crystal compositions that use a compound having a positive Δ∈ represented by formula (A-1) or (A-2) as a constitutional component of the liquid crystal composition have been disclosed (PTL 1 and PTL 2). However, these liquid crystal compositions did not achieve sufficiently low viscosity. There have also been disclosure of compounds having a —CF2O— linking group represented by formulae (A-3) and (A-4) and liquid crystal compositions that use these compounds. However, these liquid crystal compositions also did not achieve sufficiently low viscosity (PTL 3 and PTL 4).
